Adobe and Yahoo are teaming up to trial putting advertisements inside PDF documents.

Ads for Adobe PDF Powered by Yahoo, as the new service is known, presents publishers with an alternative to conventional subscriptions, which, if widely adopted, could open up a new model based on free, ad-supported publishing, say analysts. The service allows publishers to generate revenue by including text-based ads linked to the specific content of an Adobe PDF page. The advertisements can only run in a side panel separated from the publication's actual content.

"People want content for free," says Matt Swain, an analyst at market research firm at InfoTrends, who has been briefed by the companies on their plans. "The question is how do I reach consumers without charging them a subscription fee?" he says.